Modify isolate proto to have UI key

appengine/isolate/proto/config.proto

 // Copyright 2017 The LUCI Authors. All rights reserved.
 // Use of this source code is governed under the Apache License, Version 2.0
 // that can be found in the LICENSE file.
 
 syntax = "proto2";
 
 
 // Schema for settings.cfg service config file in luci-config.
 message SettingsCfg {
   // id to inject into pages if applicable.
@@ skipping 22 matching lines @@
   optional string gs_bucket = 4;
 
   // Email address of Service account used to access Google Storage.
   optional string gs_client_id_email = 5;
 
   // Enable ts_mon based monitoring. Default: False.
   optional bool enable_ts_monitoring = 6;
 
   // Names of the authorization groups used by components/auth.
   optional AuthSettings auth = 7;
+
+  // oauth client id for the ui. This is created in the developer's console
+  // under Credentials.
+  optional string ui_client_id = 8;
 }
 
 // Access control groups for the isolate service. Custom group names
 // allow several isolate server instances to co-exist under the same
 // "auth" server.
 //
 // All groups default to 'administrators'.
 message AuthSettings {
   // Group with read and write access.
   optional string full_access_group = 1;
   // Group with read-only access.
   optional string readonly_access_group = 2;
 }